Induction melting generally involves heating a metal in a crucible made from a non-conductive refractory alloy oxide until the charge of metal within the crucible is melted down to liquid form. When melting highly reactive metals such as titanium or titanium alloys, vacuum induction melting using cold wall or graphite crucibles is typically employed.
However, difficulties can arise when melting these highly reactive alloys due to the reactivity of the elements in the alloy at the temperatures needed for melting to occur. As previously mentioned, while most induction melting systems use refractory alloy oxides for crucibles in the induction furnace, alloys such as titanium aluminide (TiAl) are so highly reactive that they can attack the refractory alloys present in the crucible and contaminate the titanium alloy. For example, ceramic crucibles are typically avoided because the highly reactive alloys can break down the crucible and contaminate the titanium alloy with oxygen. Similarly, if graphite crucibles are employed, both the titanium and the aluminide can dissolve large quantities of carbon from the crucible into the titanium alloy, thereby resulting in contamination. Such contamination results in the loss of mechanical properties of the titanium alloy.
Moreover, while cold crucible melting offers metallurgical advantages for the processing of the highly reactive alloys described previously, it also has a number of technical and economic limitations including low superheat, yield losses due to skull formation, high power requirements and a limited melt capacity. These limitations can restrict its commercial viability.
Accordingly, there remains a need for methods for reducing carbon contamination when melting highly reactive alloys that can also pose fewer technical and economic limitations than current applications.